A power outage in downtown Rockville disrupted power to about 1,500 customers Thursday, including Montgomery County’s main offices.

Pepco first got a call about the outage at about 11 a.m., said Marcus Beal, Pepco spokesman.

“We have crews on site,” he said. Beal said Pepco had “an event” outside of the Rockville substation affecting two feeders serving the city.

“We are expecting to restore power by 2:30 p.m.,” he said.

As of 4 p.m., about 330 customers were still without power, according to Pepco’s outage map.

Jenny Kimball, Rockville assistant city manager, said a feeder out of the Rockville Substation tripped this morning due to a cable fault at 110 N. Washington Street.

Montgomery County’s main data servers went down with the outage, rendering the county’s website, email, voicemail and 311 call center inoperable. The servers are housed in the County Council building on Maryland Avenue.

County 911 system, police, fire, traffic systems and county lights were all not affected by the outage.

Power was restored to the county’s building by 2:20 p.m. and county data servers were gradually bringing voicemail, email and the website back into operation, county spokesman Patrick Lacefield said.

The county initially estimated it would have its servers back up by about 2 p.m.

Lacefield, who was working out of the Rockville Library at the time, said county officials were doing business “the old-fashioned way,” in person and by using cell phones, while the servers were down. They were also pushing information to the public via Facebook and Twitter.

Lacefield said he understands that the power outage took out Pepco feeders in Rockville including the one that powers the county’s data system.

But the root of the problem, for the county, appeared to lie with a transfer switch that normally would have kicked on backup generators, but today had failed, Lacefield said.

“There is something wrong with the transfer switch,” he said, adding that the switch had just been inspected a few weeks ago. “It’s not uncommon for power to surge or there to be a flicker, and always when that happens, there is a switch that switches on to generators.”

But today the generators did not flick on. As of 4 p.m., the county website was still not working.

Lacefield said the servers will come back when Pepco restores power, or when the county is able to repair or replace the switch. He said Pepco workers were in a manhole working on the problem as of about 2 p.m.

In Rockville Town Square, outages left a patchwork — some buildings without power, others with power.

Stores on Gibbs Street were among those without power, including Dawson’s Market and several restaurants.

Tommy Langford, director of operations for Dawson’s, said he saw a manhole cover located on the sidewalk of North Washington Street in front of Parking Garage C blown off the ground by the force of a small explosion of some kind.

“The manhole cover just blew up, and black smoke came out of the ground,” he said.

Employees at Dawson’s covered produce and refrigerated foods with tarps until the power came back on. Power was restored there in about an hour. Langford said the Montgomery County Health Department requires refrigerated foods to be thrown out after four hours of non-refrigeration.

Kimberly Kim, manager of Town Square Cleaners on Gibbs Street, said she just waiting for power to return.

“It is just terrible; our businesses were messed up,” she said.

The lights flickered briefly at Rockville City Hall, but the building did not lose power, Kimball said.

Rockville Police Maj. Bob Rappoport said the police station lost power briefly.